A pettern of four blastomere groups on each side develops at the 512-cell stage in the embryo of the frog, Xenopus, and the decendants of each blastomere group exclusively populate a single morphological domain, called a compartment. Descendants of each blastomere group mingle with one another but do not mingle with decendants of other blastomere groups. The aim of these experiments is to analyze these restrictions of cell mingling in vitro. The hypotheses to be tested are that the factors that restrict cell mingling are (1) differential cell adhesivity, which favors selective aggregation of cells belonging to the same compartment (2) mutual inhibition of cell motility when cells of different compartments contact one another (3) inhibition of cell division and/or cell survival when cells of different compartment contact one another. Three kinds of experiments will be done in which a blastomere group from a labelled embryo and from an unlabelled embryo will be combined in vitro, either as coherent groups of cells or after disaggregation, mixing and reaggregation. The final spatial arrangements of labelled and unlabelled cells and the numbers of labelled and unlabelled cells will be analyzed in relation to the origins of the cells from the same or from different compartments. The questions to be answered are: (1) how are cells that originate from different blastomere groups (therefore belonging to different compartments in the intact embryo) restricted from mingling in vitro? (as has been found in preliminary experiments). (2) After mixing cells derived from the same or different blastomere groups, does sorting out occur according to compartmental affiliation? (3) Is cell division and/or cell survival regulated by interactions between cells of the same or different compartmental affiliation? Do cells proliferate and/or survive at different rates when mixed with other cells belonging to the same compartment compared with their rate of proliferation and/or survival when mixed with cells of other compartments? These experiments are primarily designed to test the hypothesis that clonal restriction of cell mingling results in compartmentation during normal development. Some preliminary work will establish whether the final numbers of cells in the combinations or aggregates are related to interactions between cells of different compartmental origin.